Sonar object detection system

ABSTRACT

An airborne sonar collision avoidance system is disclosed. The system compensates for changes in temperature in real time to provide more accurate sonar detection. In addition, the sensors are arranged in a communications network that allows for the sensors to be programmed at run time, thus providing the ability to relocate the sensors without having to pre-program the sensors before the sensors are installed onto a different location.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/630,214,filed Jul. 30, 2003, and claims the benefit of U.S. ProvisionalApplication No. 60/412,350, filed on Sep. 20, 2002, entitled “SonarObject Detection System”, the contents of each of which are incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to ultrasonic systems and moreparticularly to an airborne sonar detection system.

BACKGROUND

Ultrasonic ranging systems use airborne high frequency sound waves todetect target objects. In these systems, high frequency sound waves aregenerated and transmitted to an object. The transmitted sound waves thenbounce off the object and return to their source as an echo. Thedistance from the source of the sound waves to the object can then bemeasured based on the speed of sound and the time it takes for the soundwave to travel to an object and return to the source.

Although ultrasonic sound with frequencies ranging from 20 to 200 kHzcan be used for a wide variety of ranging and sensing applications, whendesigning an ultrasonic-based system, a great care must be taken tocompensate for the many variables involved. An example of such variablesincludes dynamic temperature changes in the atmosphere. If atmospherictemperature is not properly compensated for, an erratic system operationwill result. An uncompensated system could, for example, exhibitundesirable traits such as a range that varies, blind spots, movingblind spots, a target that is detected one time and not the next,unwanted target acquisitions, and false target acquisitions.

In addition, a reliable ultrasonic system needs to account for acousticproperties that are affected by the environmental dynamics. Suchacoustic properties include variation in the speed and wavelength ofsound in air over temperature; variation in sound attenuation based onfrequency, temperature, and humidity and over distance; variation in thereturn echo, target strength, based on target distance, shape andcomposition; turbulence in the detection zone; effects of backgroundnoise; and sound radiating pattern, beam angle, of the selectedultrasonic transducer.

For example, speed of sound varies from 1041 feet/second (“ft/sec”) at−10 degrees Fahrenheit (“F”) to 1172 ft/sec at 110 F. This presents achange of 12.5% and would result in an apparent change in measurement of2.5 ft over a 20 ft distance. Further, wavelength is defined as thespeed of sound in inches/second (“in/sec”) divided by frequency, w1=c/f.Since the speed of sound, c, changes over temperature so does thewavelength. Solving for wavelength, it can be seen that a 40 kHz signalat −10 F has a wavelength of 0.3123 inch, while at +110 F, thewavelength is 0.3516 inch. For reflection to occur, the wavelengthshould be small compared to the dimension of the target because thelarger the target in comparison to wavelength, the stronger the return.Thus it can be seen that as temperature goes up, wavelength goes up andthe amount of reflection goes down. That is, the target strengthdiminishes.

Sound propagates through air by causing air molecules to collide witheach other pushing the sound along like a wall of dominoes. As soundtravels through air, these collisions result in friction loss, higherfrequency means more collisions, hence greater loss. Complicating theissue is the fact that density and composition of the medium varies withtemperature and humidity. Further, the medium behaves differently above50 kHz. A useful approximation for figuring maximum attenuation up to 50kHz and above 50 kHz may be used. While useful for approximating maximumranges, however, the actual temperature humidity attenuation is highlynon-linear. Accordingly, this attenuation also needs to be compensatedfor or target strength will vary radically over temperature causingerratic target acquisition.

As described above, because both sound and target objects have complexproperties, many considerations need to be taken into account whenbuilding an ultrasonic system. Accordingly, there is a need for aproperly designed ultrasonic system that compensates for theenvironmental factors such as dynamic temperature changes.

SUMMARY

There is provided a sonar detection system and method that compensatesfor dynamic temperature changes in real time. In one aspect, the methodincludes an object detection model residing in a sensor. The modelcompensates for atmospheric changes that result from environmentaldynamics. For example, an air density model outputs air densitydepending on the temperature. From this air density output, a gain modelcomputes amount of gain used for processing a received echo signal. Athermistor and resistor network is added to a feedback loop of a preampand causes the preamp to automatically change gain with temperatureaccording to the output of the air density and gain models.

In another aspect, the ultrasonic detection system includes acontroller, and a plurality of sensors. The controller is connected to adata input of a first one of the plurality of sensors. A data output ofthe first one of the plurality of sensors is connected to a data inputof a second one of the plurality of sensors, such that the subsequentsensors in the plurality are connected via data output of one to datainput of another. The controller polls for addresses and configures themfor the sensors in real time, thus allowing the addresses of the sensorsto change.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an ultrasonic sensor in one embodiment ofthe present invention that compensates for atmospheric temperature inreal time.

FIG. 2 is a flow diagram illustrating a method of detecting objects,compensating for temperature in real time, in one embodiment of thepresent invention.

FIG. 3 is an electrical schematic circuit diagram of a drive circuit inone embodiment of the present invention for controlling output soundpressure level in an ultrasonic transducer.

FIG. 4 is a flow diagram illustrating the method of controlling outputsound pressure level in an ultrasonic transducer in one embodiment ofthe present invention.

FIG. 5 is a communications network diagram illustrating the sensornetwork in one embodiment of the present invention.

FIG. 6 is a graph illustrating plotted air density data output from anair density model.

FIG. 7 is a graph illustrating plotted gain data output from a gainmodel.

FIG. 8 is a schematic circuit diagram illustrating an intelligent sensorin one embodiment.

FIG. 9 is a schematic diagram illustrating an individual sensor shown inFIG. 5.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of an ultrasonic sensor in one embodiment ofthe present invention that compensates for atmospheric temperature inreal time. A sensor 102 is connected to a controller 104 by, forexample, a bus 116. The sensor 102 may also communicate to thecontroller wirelessly. The sensor 102 includes a transducer 106 thatoutputs sound waves as directed by the drive 108. The sensor 102 alsoreceives sound wave echoes from an object, that is, the sound waves thatbounce back after hitting an object. The sensor 102 in one aspect mayinclude separate transducers for transmitting and receiving sound waves.

A variable gain pre-amplifier 115 receives echo signals from thetransducer 106. The variable gain pre-amplifier provides real timecompensating for environment dynamics such as the environmenttemperature. A filter 112 filters the amplified echo signals. Thefiltered echo signals are then input to an amp 114. The amp 114amplifies the signals and outputs the amplified signals to amicroprocessor 110. An object detection algorithm may reside in thesensor 102, for example, in the microprocessor 110. The microprocessor110 computes distances of objects using the received echo signals andthe time duration between the transmission of sound waves and receipt ofecho signals. The microprocessor 110 may use an air density and gainmodels to determine how much gain is used on the received signal as afunction of temperature.

The microprocessor 110 outputs the computed data such as distances, forexample, via the data bus 116, to a controller 104. The controller thenalerts a user, for example using a user interface such as displays andsound alerts, that objects are nearby. The controller 104, for example,includes a microprocessor 120 for processing data received or to betransmitted to the sensor 102, user interface functions, input/output(“I/O”) functions, etc. The controller 104 also may include atransmitter/receiver 122 for communicating data to the sensor 102. Thetransmitter/receiver 122 may be a wired or wireless transceiver. Thealert means 126 may include an alarm or a display interface for alertingor informing a user about the objects detected by the sensor 102. TheI/O 124 performs typical input/output functions. The controller 104 mayinclude a bus interface 128 for communicating data or control signalsamong the microprocessor 120, transceiver 122, I/O 124, and alert means126. The typical functions of microprocessor, transceiver, I/O, alarms,and user interfaces are generally known to those skilled in the art andtherefore, will not be described in further detail here. The controller104 generally controls how individual sensors 102 should operate.

FIG. 2 is a flow diagram illustrating a method of detecting objects,compensating for temperature in real time, in one embodiment of thepresent invention. At 202, transformed sound waves are transmitted andecho signals are received. The echo signals are filtered and amplifiedat 204. The signals are then input to a microprocessor that computes thedistance of a detected object using the information about the echoedsignals such as the time it took for the echoed signal to be reflectedback to the transducer.

At 206, using an air density and gain model that adjusts the gain on thereceived echo signals, the distance of an object is computed and thusobject is detected. At 208, the detected data is transmitted to acontroller. At 210, the controller generates an alert or otherwiseinforms a user of the detected object, for example, by a displaying thedata on a user interface or other visual warnings or by audio warningssuch as beeping alarm or voice activated alarm.

As described above, in one aspect, atmospheric and gain models are usedto compensate the atmospheric changes, for example, temperature.Although the atmosphere is in constant motion and is inhomogeneous,useful approximations may be formed if the variations in the medium aresmall with respect to the wavelength. In one aspect, the ideal gas lawsof Charles and Boyle are used to calculate air density, with a basicassumption that the atmosphere within the range of technology is stableduring this very short time of flight of the sound waves. The ideal gaslaw takes the base form of PV-nRT, where P=pressure, V=volume, n=molevolume of gas, R=the gas constant, and T=temperature. The formula fordensity is derived as D=P/T*R. Gas constants are published in mostchemistry texts. The value of R for dry air is 287. With pressureassumed to be constant, in this case barometric pressure at sea level,and temperature varied, the values shown in Table 1 result. TABLE 1Atmospheric pressure data (at sea level) based on temperature andhumidity Data is based on published values of H₂O saturation vaporpressure Calculations are based on the law of partial pressures and theideal gas law Temperature for this humidity data is 0 degrees f. At arelative humidity of 0 percent, the air density at sea level is 1.38249kg/m{circumflex over ( )}3 At a relative humidity of 10 percent, the airdensity at sea level is 1.38241 kg/m{circumflex over ( )}3 At a relativehumidity of 20 percent, the air density at sea level is 1.38233kg/m{circumflex over ( )}3 At a relative humidity of 30 percent, the airdensity at sea level is 1.38225 kg/m{circumflex over ( )}3 At a relativehumidity of 40 percent, the air density at sea level is 1.38218kg/m{circumflex over ( )}3 At a relative humidity of 50 percent, the airdensity at sea level is 1.3821 kg/m{circumflex over ( )}3 At a relativehumidity of 60 percent, the air density at sea level is 1.38202kg/m{circumflex over ( )}3 At a relative humidity of 70 percent, the airdensity at sea level is 1.38195 kg/m{circumflex over ( )}3 At a relativehumidity of 80 percent, the air density at sea level is 1.38187kg/m{circumflex over ( )}3 At a relative humidity of 90 percent, the airdensity at sea level is 1.38179 kg/m{circumflex over ( )}3 At a relativehumidity of 100 percent, the air density at sea level is 1.38171kg/m{circumflex over ( )}3 Temperature for this humidity data is 5degrees f. At a relative humidity of 0 percent, the air density at sealevel is 1.36761 kg/m{circumflex over ( )}3 At a relative humidity of 10percent, the air density at sea level is 1.36751 kg/m{circumflex over( )}3 At a relative humidity of 20 percent, the air density at sea levelis 1.36742 kg/m{circumflex over ( )}3 At a relative humidity of 30percent, the air density at sea level is 1.36732 kg/m{circumflex over( )}3 At a relative humidity of 40 percent, the air density at sea levelis 1.36722 kg/m{circumflex over ( )}3 At a relative humidity of 50percent, the air density at sea level is 1.36713 kg/m{circumflex over( )}3 At a relative humidity of 60 percent, the air density at sea levelis 1.36703 kg/m{circumflex over ( )}3 At a relative humidity of 70percent, the air density at sea level is 1.36693 kg/m{circumflex over( )}3 At a relative humidity of 80 percent, the air density at sea levelis 1.36684 kg/m{circumflex over ( )}3 At a relative humidity of 90percent, the air density at sea level is 1.36674 kg/m{circumflex over( )}3 At a relative humidity of 100 percent, the air density at sealevel is 1.36664 kg/m{circumflex over ( )}3 Temperature for thishumidity data is 10 degrees f. At a relative humidity of 0 percent, theair density at sea level is 1.35305 kg/m{circumflex over ( )}3 At arelative humidity of 10 percent, the air density at sea level is 1.35293kg/m{circumflex over ( )}3 At a relative humidity of 20 percent, the airdensity at sea level is 1.35281 kg/m{circumflex over ( )}3 At a relativehumidity of 30 percent, the air density at sea level is 1.35269kg/m{circumflex over ( )}3 At a relative humidity of 40 percent, the airdensity at sea level is 1.35257 kg/m{circumflex over ( )}3 At a relativehumidity of 50 percent, the air density at sea level is 1.35245kg/m{circumflex over ( )}3 At a relative humidity of 60 percent, the airdensity at sea level is 1.35232 kg/m{circumflex over ( )}3 At a relativehumidity of 70 percent, the air density at sea level is 1.3522kg/m{circumflex over ( )}3 At a relative humidity of 80 percent, the airdensity at sea level is 1.35208 kg/m{circumflex over ( )}3 At a relativehumidity of 90 percent, the air density at sea level is 1.35196kg/m{circumflex over ( )}3 At a relative humidity of 100 percent, theair density at sea level is 1.35184 kg/m{circumflex over ( )}3Temperature for this humidity data is 15 degrees f. At a relativehumidity of 0 percent, the air density at sea level is 1.3388kg/m{circumflex over ( )}3 At a relative humidity of 10 percent, the airdensity at sea level is 1.33865 kg/m{circumflex over ( )}3 At a relativehumidity of 20 percent, the air density at sea level is 1.3385kg/m{circumflex over ( )}3 At a relative humidity of 30 percent, the airdensity at sea level is 1.33835 kg/m{circumflex over ( )}3 At a relativehumidity of 40 percent, the air density at sea level is 1.3382kg/m{circumflex over ( )}3 At a relative humidity of 50 percent, the airdensity at sea level is 1.33805 kg/m{circumflex over ( )}3 At a relativehumidity of 60 percent, the air density at sea level is 1.3379kg/m{circumflex over ( )}3 At a relative humidity of 70 percent, the airdensity at sea level is 1.33775 kg/m{circumflex over ( )}3 At a relativehumidity of 80 percent, the air density at sea level is 1.3376kg/m{circumflex over ( )}3 At a relative humidity of 90 percent, the airdensity at sea level is 1.33745 kg/m{circumflex over ( )}3 At a relativehumidity of 100 percent, the air density at sea level is 1.3373kg/m{circumflex over ( )}3 Temperature for this humidity data is 20degrees f. At a relative humidity of 0 percent, the air density at sealevel is 1.32484 kg/m{circumflex over ( )}3 At a relative humidity of 10percent, the air density at sea level is 1.32466 kg/m{circumflex over( )}3 At a relative humidity of 20 percent, the air density at sea levelis 1.32448 kg/m{circumflex over ( )}3 At a relative humidity of 30percent, the air density at sea level is 1.32429 kg/m{circumflex over( )}3 At a relative humidity of 40 percent, the air density at sea levelis 1.32411 kg/m{circumflex over ( )}3 At a relative humidity of 50percent, the air density at sea level is 1.32393 kg/m{circumflex over( )}3 At a relative humidity of 60 percent, the air density at sea levelis 1.32375 kg/m{circumflex over ( )}3 At a relative humidity of 70percent, the air density at sea level is 1.32356 kg/m{circumflex over( )}3 At a relative humidity of 80 percent, the air density at sea levelis 1.32338 kg/m{circumflex over ( )}3 At a relative humidity of 90percent, the air density at sea level is 1.3232 kg/m{circumflex over( )}3 At a relative humidity of 100 percent, the air density at sealevel is 1.32301 kg/m{circumflex over ( )}3 Temperature for thishumidity data is 25 degrees f. At a relative humidity of 0 percent, theair density at sea level is 1.31118 kg/m{circumflex over ( )}3 At arelative humidity of 10 percent, the air density at sea level is 1.31095kg/m{circumflex over ( )}3 At a relative humidity of 20 percent, the airdensity at sea level is 1.31073 kg/m{circumflex over ( )}3 At a relativehumidity of 30 percent, the air density at sea level is 1.3105kg/m{circumflex over ( )}3 At a relative humidity of 40 percent, the airdensity at sea level is 1.31028 kg/m{circumflex over ( )}3 At a relativehumidity of 50 percent, the air density at sea level is 1.31005kg/m{circumflex over ( )}3 At a relative humidity of 60 percent, the airdensity at sea level is 1.30983 kg/m{circumflex over ( )}3 At a relativehumidity of 70 percent, the air density at sea level is 1.3096kg/m{circumflex over ( )}3 At a relative humidity of 80 percent, the airdensity at sea level is 1.30938 kg/m{circumflex over ( )}3 At a relativehumidity of 90 percent, the air density at sea level is 1.30915kg/m{circumflex over ( )}3 At a relative humidity of 100 percent, theair density at sea level is 1.30893 kg/m{circumflex over ( )}3Temperature for this humidity data is 30 degrees f. At a relativehumidity of 0 percent, the air density at sea level is 1.29779kg/m{circumflex over ( )}3 At a relative humidity of 10 percent, the airdensity at sea level is 1.29752 kg/m{circumflex over ( )}3 At a relativehumidity of 20 percent, the air density at sea level is 1.29725kg/m{circumflex over ( )}3 At a relative humidity of 30 percent, the airdensity at sea level is 1.29697 kg/m{circumflex over ( )}3 At a relativehumidity of 40 percent, the air density at sea level is 1.2967kg/m{circumflex over ( )}3 At a relative humidity of 50 percent, the airdensity at sea level is 1.29643 kg/m{circumflex over ( )}3 At a relativehumidity of 60 percent, the air density at sea level is 1.29616kg/m{circumflex over ( )}3 At a relative humidity of 70 percent, the airdensity at sea level is 1.29589 kg/m{circumflex over ( )}3 At a relativehumidity of 80 percent, the air density at sea level is 1.29562kg/m{circumflex over ( )}3 At a relative humidity of 90 percent, the airdensity at sea level is 1.29535 kg/m{circumflex over ( )}3 At a relativehumidity of 100 percent, the air density at sea level is 1.29508kg/m{circumflex over ( )}3 Temperature for this humidity data is 35degrees f. At a relative humidity of 0 percent, the air density at sealevel is 1.28467 kg/m{circumflex over ( )}3 At a relative humidity of 10percent, the air density at sea level is 1.28434 kg/m{circumflex over( )}3 At a relative humidity of 20 percent, the air density at sea levelis 1.28401 kg/m{circumflex over ( )}3 At a relative humidity of 30percent, the air density at sea level is 1.28368 kg/m{circumflex over( )}3 At a relative humidity of 40 percent, the air density at sea levelis 1.28335 kg/m{circumflex over ( )}3 At a relative humidity of 50percent, the air density at sea level is 1.28302 kg/m{circumflex over( )}3 At a relative humidity of 60 percent, the air density at sea levelis 1.28269 kg/m{circumflex over ( )}3 At a relative humidity of 70percent, the air density at sea level is 1.28235 kg/m{circumflex over( )}3 At a relative humidity of 80 percent, the air density at sea levelis 1.28202 kg/m{circumflex over ( )}3 At a relative humidity of 90percent, the air density at sea level is 1.28169 kg/m{circumflex over( )}3 At a relative humidity of 100 percent, the air density at sealevel is 1.28136 kg/m{circumflex over ( )}3 Temperature for thishumidity data is 40 degrees f. At a relative humidity of 0 percent, theair density at sea level is 1.27181 kg/m{circumflex over ( )}3 At arelative humidity of 10 percent, the air density at sea level is 1.27142kg/m{circumflex over ( )}3 At a relative humidity of 20 percent, the airdensity at sea level is 1.27102 kg/m{circumflex over ( )}3 At a relativehumidity of 30 percent, the air density at sea level is 1.27062kg/m{circumflex over ( )}3 At a relative humidity of 40 percent, the airdensity at sea level is 1.27022 kg/m{circumflex over ( )}3 At a relativehumidity of 50 percent, the air density at sea level is 1.26982kg/m{circumflex over ( )}3 At a relative humidity of 60 percent, the airdensity at sea level is 1.26942 kg/m{circumflex over ( )}3 At a relativehumidity of 70 percent, the air density at sea level is 1.26902kg/m{circumflex over ( )}3 At a relative humidity of 80 percent, the airdensity at sea level is 1.26863 kg/m{circumflex over ( )}3 At a relativehumidity of 90 percent, the air density at sea level is 1.26823kg/m{circumflex over ( )}3 At a relative humidity of 100 percent, theair density at sea level is 1.26783 kg/m{circumflex over ( )}3Temperature for this humidity data is 45 degrees f. At a relativehumidity of 0 percent, the air density at sea level is 1.25921kg/m{circumflex over ( )}3 At a relative humidity of 10 percent, the airdensity at sea level is 1.25874 kg/m{circumflex over ( )}3 At a relativehumidity of 20 percent, the air density at sea level is 1.25826kg/m{circumflex over ( )}3 At a relative humidity of 30 percent, the airdensity at sea level is 1.25778 kg/m{circumflex over ( )}3 At a relativehumidity of 40 percent, the air density at sea level is 1.2573kg/m{circumflex over ( )}3 At a relative humidity of 50 percent, the airdensity at sea level is 1.25682 kg/m{circumflex over ( )}3 At a relativehumidity of 60 percent, the air density at sea level is 1.25634kg/m{circumflex over ( )}3 At a relative humidity of 70 percent, the airdensity at sea level is 1.25586 kg/m{circumflex over ( )}3 At a relativehumidity of 80 percent, the air density at sea level is 1.25538kg/m{circumflex over ( )}3 At a relative humidity of 90 percent, the airdensity at sea level is 1.2549 kg/m{circumflex over ( )}3 At a relativehumidity of 100 percent, the air density at sea level is 1.25442kg/m{circumflex over ( )}3 Temperature for this humidity data is 50degrees f. At a relative humidity of 0 percent, the air density at sealevel is 1.24686 kg/m{circumflex over ( )}3 At a relative humidity of 10percent, the air density at sea level is 1.24629 kg/m{circumflex over( )}3 At a relative humidity of 20 percent, the air density at sea levelis 1.24572 kg/m{circumflex over ( )}3 At a relative humidity of 30percent, the air density at sea level is 1.24514 kg/m{circumflex over( )}3 At a relative humidity of 40 percent, the air density at sea levelis 1.24457 kg/m{circumflex over ( )}3 At a relative humidity of 50percent, the air density at sea level is 1.244 kg/m{circumflex over( )}3 At a relative humidity of 60 percent, the air density at sea levelis 1.24343 kg/m{circumflex over ( )}3 At a relative humidity of 70percent, the air density at sea level is 1.24286 kg/m{circumflex over( )}3 At a relative humidity of 80 percent, the air density at sea levelis 1.24228 kg/m{circumflex over ( )}3 At a relative humidity of 90percent, the air density at sea level is 1.24171 kg/m{circumflex over( )}3 At a relative humidity of 100 percent, the air density at sealevel is 1.24114 kg/m{circumflex over ( )}3 Temperature for thishumidity data is 55 degrees f. At a relative humidity of 0 percent, theair density at sea level is 1.23475 kg/m{circumflex over ( )}3 At arelative humidity of 10 percent, the air density at sea level is 1.23407kg/m{circumflex over ( )}3 At a relative humidity of 20 percent, the airdensity at sea level is 1.23338 kg/m{circumflex over ( )}3 At a relativehumidity of 30 percent, the air density at sea level is 1.2327kg/m{circumflex over ( )}3 At a relative humidity of 40 percent, the airdensity at sea level is 1.23202 kg/m{circumflex over ( )}3 At a relativehumidity of 50 percent, the air density at sea level is 1.23134kg/m{circumflex over ( )}3 At a relative humidity of 60 percent, the airdensity at sea level is 1.23066 kg/m{circumflex over ( )}3 At a relativehumidity of 70 percent, the air density at sea level is 1.22997kg/m{circumflex over ( )}3 At a relative humidity of 80 percent, the airdensity at sea level is 1.22929 kg/m{circumflex over ( )}3 At a relativehumidity of 90 percent, the air density at sea level is 1.22861kg/m{circumflex over ( )}3 At a relative humidity of 100 percent, theair density at sea level is 1.22793 kg/m{circumflex over ( )}3Temperature for this humidity data is 60 degrees f. At a relativehumidity of 0 percent, the air density at sea level is 1.22287kg/m{circumflex over ( )}3 At a relative humidity of 10 percent, the airdensity at sea level is 1.22206 kg/m{circumflex over ( )}3 At a relativehumidity of 20 percent, the air density at sea level is 1.22125kg/m{circumflex over ( )}3 At a relative humidity of 30 percent, the airdensity at sea level is 1.22044 kg/m{circumflex over ( )}3 At a relativehumidity of 40 percent, the air density at sea level is 1.21964kg/m{circumflex over ( )}3 At a relative humidity of 50 percent, the airdensity at sea level is 1.21883 kg/m{circumflex over ( )}3 At a relativehumidity of 60 percent, the air density at sea level is 1.21802kg/m{circumflex over ( )}3 At a relative humidity of 70 percent, the airdensity at sea level is 1.21721 kg/m{circumflex over ( )}3 At a relativehumidity of 80 percent, the air density at sea level is 1.21641kg/m{circumflex over ( )}3 At a relative humidity of 90 percent, the airdensity at sea level is 1.2156 kg/m{circumflex over ( )}3 At a relativehumidity of 100 percent, the air density at sea level is 1.21479kg/m{circumflex over ( )}3 Temperature for this humidity data is 65degrees f. At a relative humidity of 0 percent, the air density at sealevel is 1.21121 kg/m{circumflex over ( )}3 At a relative humidity of 10percent, the air density at sea level is 1.21027 kg/m{circumflex over( )}3 At a relative humidity of 20 percent, the air density at sea levelis 1.20932 kg/m{circumflex over ( )}3 At a relative humidity of 30percent, the air density at sea level is 1.20837 kg/m{circumflex over( )}3 At a relative humidity of 40 percent, the air density at sea levelis 1.20742 kg/m{circumflex over ( )}3 At a relative humidity of 50percent, the air density at sea level is 1.20647 kg/m{circumflex over( )}3 At a relative humidity of 60 percent, the air density at sea levelis 1.20552 kg/m{circumflex over ( )}3 At a relative humidity of 70percent, the air density at sea level is 1.20457 kg/m{circumflex over( )}3 At a relative humidity of 80 percent, the air density at sea levelis 1.20362 kg/m{circumflex over ( )}3 At a relative humidity of 90percent, the air density at sea level is 1.20267 kg/m{circumflex over( )}3 At a relative humidity of 100 percent, the air density at sealevel is 1.20172 kg/m{circumflex over ( )}3 Temperature for thishumidity data is 70 degrees f. At a relative humidity of 0 percent, theair density at sea level is 1.19978 kg/m{circumflex over ( )}3 At arelative humidity of 10 percent, the air density at sea level is 1.19866kg/m{circumflex over ( )}3 At a relative humidity of 20 percent, the airdensity at sea level is 1.19754 kg/m{circumflex over ( )}3 At a relativehumidity of 30 percent, the air density at sea level is 1.19642kg/m{circumflex over ( )}3 At a relative humidity of 40 percent, the airdensity at sea level is 1.1953 kg/m{circumflex over ( )}3 At a relativehumidity of 50 percent, the air density at sea level is 1.19418kg/m{circumflex over ( )}3 At a relative humidity of 60 percent, the airdensity at sea level is 1.19306 kg/m{circumflex over ( )}3 At a relativehumidity of 70 percent, the air density at sea level is 1.19195kg/m{circumflex over ( )}3 At a relative humidity of 80 percent, the airdensity at sea level is 1.19083 kg/m{circumflex over ( )}3 At a relativehumidity of 90 percent, the air density at sea level is 1.18971kg/m{circumflex over ( )}3 At a relative humidity of 100 percent, theair density at sea level is 1.18859 kg/m{circumflex over ( )}3Temperature for this humidity data is 75 degrees f. At a relativehumidity of 0 percent, the air density at sea level is 1.18856kg/m{circumflex over ( )}3 At a relative humidity of 10 percent, the airdensity at sea level is 1.18725 kg/m{circumflex over ( )}3 At a relativehumidity of 20 percent, the air density at sea level is 1.18594kg/m{circumflex over ( )}3 At a relative humidity of 30 percent, the airdensity at sea level is 1.18462 kg/m{circumflex over ( )}3 At a relativehumidity of 40 percent, the air density at sea level is 1.18331kg/m{circumflex over ( )}3 At a relative humidity of 50 percent, the airdensity at sea level is 1.182 kg/m{circumflex over ( )}3 At a relativehumidity of 60 percent, the air density at sea level is 1.18068kg/m{circumflex over ( )}3 At a relative humidity of 70 percent, the airdensity at sea level is 1.17937 kg/m{circumflex over ( )}3 At a relativehumidity of 80 percent, the air density at sea level is 1.17806kg/m{circumflex over ( )}3 At a relative humidity of 90 percent, the airdensity at sea level is 1.17675 kg/m{circumflex over ( )}3 At a relativehumidity of 100 percent, the air density at sea level is 1.17543kg/m{circumflex over ( )}3 Temperature for this humidity data is 80degrees f. At a relative humidity of 0 percent, the air density at sealevel is 1.17755 kg/m{circumflex over ( )}3 At a relative humidity of 10percent, the air density at sea level is 1.17601 kg/m{circumflex over( )}3 At a relative humidity of 20 percent, the air density at sea levelis 1.17447 kg/m{circumflex over ( )}3 At a relative humidity of 30percent, the air density at sea level is 1.17293 kg/m{circumflex over( )}3 At a relative humidity of 40 percent, the air density at sea levelis 1.1714 kg/m{circumflex over ( )}3 At a relative humidity of 50percent, the air density at sea level is 1.16986 kg/m{circumflex over( )}3 At a relative humidity of 60 percent, the air density at sea levelis 1.16832 kg/m{circumflex over ( )}3 At a relative humidity of 70percent, the air density at sea level is 1.16678 kg/m{circumflex over( )}3 At a relative humidity of 80 percent, the air density at sea levelis 1.16524 kg/m{circumflex over ( )}3 At a relative humidity of 90percent, the air density at sea level is 1.16371 kg/m{circumflex over( )}3 At a relative humidity of 100 percent, the air density at sealevel is 1.16217 kg/m{circumflex over ( )}3 Temperature for thishumidity data is 85 degrees f. At a relative humidity of 0 percent, theair density at sea level is 1.16674 kg/m{circumflex over ( )}3 At arelative humidity of 10 percent, the air density at sea level is 1.16495kg/m{circumflex over ( )}3 At a relative humidity of 20 percent, the airdensity at sea level is 1.16317 kg/m{circumflex over ( )}3 At a relativehumidity of 30 percent, the air density at sea level is 1.16138kg/m{circumflex over ( )}3 At a relative humidity of 40 percent, the airdensity at sea level is 1.1596 kg/m{circumflex over ( )}3 At a relativehumidity of 50 percent, the air density at sea level is 1.15781kg/m{circumflex over ( )}3 At a relative humidity of 60 percent, the airdensity at sea level is 1.15603 kg/m{circumflex over ( )}3 At a relativehumidity of 70 percent, the air density at sea level is 1.15424kg/m{circumflex over ( )}3 At a relative humidity of 80 percent, the airdensity at sea level is 1.15246 kg/m{circumflex over ( )}3 At a relativehumidity of 90 percent, the air density at sea level is 1.15067kg/m{circumflex over ( )}3 At a relative humidity of 100 percent, theair density at sea level is 1.14889 kg/m{circumflex over ( )}3Temperature for this humidity data is 90 degrees f. At a relativehumidity of 0 percent, the air density at sea level is 1.15613kg/m{circumflex over ( )}3 At a relative humidity of 10 percent, the airdensity at sea level is 1.15405 kg/m{circumflex over ( )}3 At a relativehumidity of 20 percent, the air density at sea level is 1.15198kg/m{circumflex over ( )}3 At a relative humidity of 30 percent, the airdensity at sea level is 1.1499 kg/m{circumflex over ( )}3 At a relativehumidity of 40 percent, the air density at sea level is 1.14783kg/m{circumflex over ( )}3 At a relative humidity of 50 percent, the airdensity at sea level is 1.14575 kg/m{circumflex over ( )}3 At a relativehumidity of 60 percent, the air density at sea level is 1.14367kg/m{circumflex over ( )}3 At a relative humidity of 70 percent, the airdensity at sea level is 1.1416 kg/m{circumflex over ( )}3 At a relativehumidity of 80 percent, the air density at sea level is 1.13952kg/m{circumflex over ( )}3 At a relative humidity of 90 percent, the airdensity at sea level is 1.13745 kg/m{circumflex over ( )}3 At a relativehumidity of 100 percent, the air density at sea level is 1.13537kg/m{circumflex over ( )}3 Temperature for this humidity data is 95degrees f. At a relative humidity of 0 percent, the air density at sealevel is 1.1457 kg/m{circumflex over ( )}3 At a relative humidity of 10percent, the air density at sea level is 1.1433 kg/m{circumflex over( )}3 At a relative humidity of 20 percent, the air density at sea levelis 1.1409 kg/m{circumflex over ( )}3 At a relative humidity of 30percent, the air density at sea level is 1.1385 kg/m{circumflex over( )}3 At a relative humidity of 40 percent, the air density at sea levelis 1.13609 kg/m{circumflex over ( )}3 At a relative humidity of 50percent, the air density at sea level is 1.13369 kg/m{circumflex over( )}3 At a relative humidity of 60 percent, the air density at sea levelis 1.13129 kg/m{circumflex over ( )}3 At a relative humidity of 70percent, the air density at sea level is 1.12888 kg/m{circumflex over( )}3 At a relative humidity of 80 percent, the air density at sea levelis 1.12648 kg/m{circumflex over ( )}3 At a relative humidity of 90percent, the air density at sea level is 1.12408 kg/m{circumflex over( )}3 At a relative humidity of 100 percent, the air density at sealevel is 1.12168 kg/m{circumflex over ( )}3 Temperature for thishumidity data is 100 degrees f. At a relative humidity of 0 percent, theair density at sea level is 1.13547 kg/m{circumflex over ( )}3 At arelative humidity of 10 percent, the air density at sea level is 1.13269kg/m{circumflex over ( )}3 At a relative humidity of 20 percent, the airdensity at sea level is 1.12991 kg/m{circumflex over ( )}3 At a relativehumidity of 30 percent, the air density at sea level is 1.12713kg/m{circumflex over ( )}3 At a relative humidity of 40 percent, the airdensity at sea level is 1.12435 kg/m{circumflex over ( )}3 At a relativehumidity of 50 percent, the air density at sea level is 1.12157kg/m{circumflex over ( )}3 At a relative humidity of 60 percent, the airdensity at sea level is 1.11879 kg/m{circumflex over ( )}3 At a relativehumidity of 70 percent, the air density at sea level is 1.11601kg/m{circumflex over ( )}3 At a relative humidity of 80 percent, the airdensity at sea level is 1.11323 kg/m{circumflex over ( )}3 At a relativehumidity of 90 percent, the air density at sea level is 1.11045kg/m{circumflex over ( )}3 At a relative humidity of 100 percent, theair density at sea level is 1.10767 kg/m{circumflex over ( )}3Temperature for this humidity data is 105 degrees f. At a relativehumidity of 0 percent, the air density at sea level is 1.12541kg/m{circumflex over ( )}3 At a relative humidity of 10 percent, the airdensity at sea level is 1.12221 kg/m{circumflex over ( )}3 At a relativehumidity of 20 percent, the air density at sea level is 1.11901kg/m{circumflex over ( )}3 At a relative humidity of 30 percent, the airdensity at sea level is 1.11581 kg/m{circumflex over ( )}3 At a relativehumidity of 40 percent, the air density at sea level is 1.11261kg/m{circumflex over ( )}3 At a relative humidity of 50 percent, the airdensity at sea level is 1.10941 kg/m{circumflex over ( )}3 At a relativehumidity of 60 percent, the air density at sea level is 1.10621kg/m{circumflex over ( )}3 At a relative humidity of 70 percent, the airdensity at sea level is 1.10301 kg/m{circumflex over ( )}3 At a relativehumidity of 80 percent, the air density at sea level is 1.09981kg/m{circumflex over ( )}3 At a relative humidity of 90 percent, the airdensity at sea level is 1.09661 kg/m{circumflex over ( )}3 At a relativehumidity of 100 percent, the air density at sea level is 1.09341kg/m{circumflex over ( )}3 Temperature for this humidity data is 110degrees f. At a relative humidity of 0 percent, the air density at sealevel is 1.11554 kg/m{circumflex over ( )}3 At a relative humidity of 10percent, the air density at sea level is 1.11188 kg/m{circumflex over( )}3 At a relative humidity of 20 percent, the air density at sea levelis 1.10823 kg/m{circumflex over ( )}3 At a relative humidity of 30percent, the air density at sea level is 1.10457 kg/m{circumflex over( )}3 At a relative humidity of 40 percent, the air density at sea levelis 1.10092 kg/m{circumflex over ( )}3 At a relative humidity of 50percent, the air density at sea level is 1.09726 kg/m{circumflex over( )}3 At a relative humidity of 60 percent, the air density at sea levelis 1.09361 kg/m{circumflex over ( )}3 At a relative humidity of 70percent, the air density at sea level is 1.08995 kg/m{circumflex over( )}3 At a relative humidity of 80 percent, the air density at sea levelis 1.0863 kg/m{circumflex over ( )}3 At a relative humidity of 90percent, the air density at sea level is 1.08264 kg/m{circumflex over( )}3 At a relative humidity of 100 percent, the air density at sealevel is 1.07899 kg/m{circumflex over ( )}3 Temperature for thishumidity data is 115 degrees f. At a relative humidity of 0 percent, theair density at sea level is 1.10583 kg/m{circumflex over ( )}3 At arelative humidity of 10 percent, the air density at sea level is 1.10165kg/m{circumflex over ( )}3 At a relative humidity of 20 percent, the airdensity at sea level is 1.09746 kg/m{circumflex over ( )}3 At a relativehumidity of 30 percent, the air density at sea level is 1.09328kg/m{circumflex over ( )}3 At a relative humidity of 40 percent, the airdensity at sea level is 1.08909 kg/m{circumflex over ( )}3 At a relativehumidity of 50 percent, the air density at sea level is 1.08491kg/m{circumflex over ( )}3 At a relative humidity of 60 percent, the airdensity at sea level is 1.08072 kg/m{circumflex over ( )}3 At a relativehumidity of 70 percent, the air density at sea level is 1.07654kg/m{circumflex over ( )}3 At a relative humidity of 80 percent, the airdensity at sea level is 1.07236 kg/m{circumflex over ( )}3 At a relativehumidity of 90 percent, the air density at sea level is 1.06817kg/m{circumflex over ( )}3 At a relative humidity of 100 percent, theair density at sea level is 1.06399 kg/m{circumflex over ( )}3Temperature for this humidity data is 120 degrees f. At a relativehumidity of 0 percent, the air density at sea level is 1.09629kg/m{circumflex over ( )}3 At a relative humidity of 10 percent, the airdensity at sea level is 1.09151 kg/m{circumflex over ( )}3 At a relativehumidity of 20 percent, the air density at sea level is 1.08674kg/m{circumflex over ( )}3 At a relative humidity of 30 percent, the airdensity at sea level is 1.08196 kg/m{circumflex over ( )}3 At a relativehumidity of 40 percent, the air density at sea level is 1.07718kg/m{circumflex over ( )}3 At a relative humidity of 50 percent, the airdensity at sea level is 1.0724 kg/m{circumflex over ( )}3 At a relativehumidity of 60 percent, the air density at sea level is 1.06762kg/m{circumflex over ( )}3 At a relative humidity of 70 percent, the airdensity at sea level is 1.06284 kg/m{circumflex over ( )}3 At a relativehumidity of 80 percent, the air density at sea level is 1.05807kg/m{circumflex over ( )}3 At a relative humidity of 90 percent, the airdensity at sea level is 1.05329 kg/m{circumflex over ( )}3 At a relativehumidity of 100 percent, the air density at sea level is 1.04851kg/m{circumflex over ( )}3 Temperature for this humidity data is 125degrees f. At a relative humidity of 0 percent, the air density at sealevel is 1.08692 kg/m{circumflex over ( )}3 At a relative humidity of 10percent, the air density at sea level is 1.08147 kg/m{circumflex over( )}3 At a relative humidity of 20 percent, the air density at sea levelis 1.07603 kg/m{circumflex over ( )}3 At a relative humidity of 30percent, the air density at sea level is 1.07059 kg/m{circumflex over( )}3 At a relative humidity of 40 percent, the air density at sea levelis 1.06514 kg/m{circumflex over ( )}3 At a relative humidity of 50percent, the air density at sea level is 1.0597 kg/m{circumflex over( )}3 At a relative humidity of 60 percent, the air density at sea levelis 1.05426 kg/m{circumflex over ( )}3 At a relative humidity of 70percent, the air density at sea level is 1.04881 kg/m{circumflex over( )}3 At a relative humidity of 80 percent, the air density at sea levelis 1.04337 kg/m{circumflex over ( )}3 At a relative humidity of 90percent, the air density at sea level is 1.03793 kg/m{circumflex over( )}3 At a relative humidity of 100 percent, the air density at sealevel is 1.03248 kg/m{circumflex over ( )}3

From a plot of this data, slope of the curve at any point may becalculated and a matching preamp gain curve generated. In this case, thestandard gain formula of the ideal non-inverting op-amp,E(o)/E(in)=R(in)+R(f)/R(in), is used. R(in) in this equation has thetemperature compensation network substituted for it. Referring to thesensor schematic of FIG. 8, E(o)/E(in) is calculated according to thefollowing equation:E(o)/E(in)=(((R16+TR1)*(R16+TR1))/((R16+TR1)+(R16+TR1)))+(R18)/(((R16+TR1)*(R16+TR1))/((R16+TR1)+(R16+TR1)))

Where TR1 changes with temperature. When calculated over temperature thevalues in Table 2 result. FIG. 6 represents the plotted data of Table 1,and FIG. 7 represents the plotted data of Table 2. TABLE 2 At −40 deg.c. with trim = 1000 thrm = 1752 fb1 = 2000 fb2 = 33000 gain = 28.54018At −35 deg. c. with trim = 1000 thrm = 1392 fb1 = 2000 fb2 = 33000 gain= 30.22285 At −30 deg. c. with trim = 1000 thrm = 1115 fb1 = 2000 fb2 =33000 gain = 31.90042 At −25 deg. c. with trim = 1000 thrm = 900 fb1 =2000 fb2 = 33000 gain = 33.53286 At −20 deg. c. with trim = 1000 thrm =732 fb1 = 2000 fb2 = 33000 gain = 35.08427 At −15 deg. c. with trim =1000 thrm = 599 fb1 = 2000 fb2 = 33000 gain = 36.53813 At −10 deg. c.with trim = 1000 thrm = 494 fb1 = 2000 fb2 = 33000 gain = 37.86408 At −5deg. c. with trim = 1000 thrm = 409 fb1 = 2000 fb2 = 33000 gain =39.0783 At 0 deg. c. with trim = 1000 thrm = 341 fb1 = 2000 fb2 = 33000gain = 40.15735 At 5 deg. c. with trim = 1000 thrm = 286 fb1 = 2000 fb2= 33000 gain = 41.11112 At 10 deg. c. with trim = 1000 thrm = 241 fb1 =2000 fb2 = 33000 gain = 41.95243 At 15 deg. c. with trim = 1000 thrm =205 fb1 = 2000 fb2 = 33000 gain = 42.66929 At 20 deg. c. with trim =1000 thrm = 175 fb1 = 2000 fb2 = 33000 gain = 43.29915 At 25 deg. c.with trim = 1000 thrm = 150 fb1 = 2000 fb2 = 33000 gain = 43.84831 At 30deg. c. with trim = 1000 thrm = 129 fb1 = 2000 fb2 = 33000 gain =44.32777 At 35 deg. c. with trim = 1000 thrm = 112 fb1 = 2000 fb2 =33000 gain = 44.72871 At 40 deg. c. with trim = 1000 thrm = 97 fb1 =2000 fb2 = 33000 gain = 45.09245 At 45 deg. c. with trim = 1000 thrm =85 fb1 = 2000 fb2 = 33000 gain = 45.39042 At 50 deg. c. with trim = 1000thrm = 75 fb1 = 2000 fb2 = 33000 gain = 45.64364 At 55 deg. c. with trim= 1000 thrm = 66 fb1 = 2000 fb2 = 33000 gain = 45.87546 At 60 deg. c.with trim = 1000 thrm = 58 fb1 = 2000 fb2 = 33000 gain = 46.08471 At 65deg. c. with trim = 1000 thrm = 52 fb1 = 2000 fb2 = 33000 gain =46.24365 At 70 deg. c. with trim = 1000 thrm = 46 fb1 = 2000 fb2 = 33000gain = 46.40436 At 75 deg. c. with trim = 1000 thrm = 41 fb1 = 2000 fb2= 33000 gain = 46.53966 At 80 deg. c. with trim = 1000 thrm = 37 fb1 =2000 fb2 = 33000 gain = 46.64879 At 85 deg. c. with trim = 1000 thrm =33 fb1 = 2000 fb2 = 33000 gain = 46.75873

The uncompensated gain is 17.17647 at trim=1000, fb1=2000, andfb2=33000. The air density and gain models compensate for changes intemperature by first modeling air density as a function of temperature.Sound travels better when air density is high, that is, air moleculesare closer together allowing for better medium for sound to travel.Accordingly, as air density goes up, gain is adjusted to be decreased.

FIG. 3 is an electrical schematic circuit diagram of a drive circuit inone embodiment of the present invention. The drive circuit 108 shown inFIG. 1, for example, may be implemented according to this circuitdiagram. This drive circuit controls output sound pressure level (“SPL”)in an ultrasonic transducer such that the sound pressure levels may bereduced at extremely low temperatures where sound travels best. That is,when the temperature is lower, air density is high, and since soundtravels better in the denser air, lower SPL may be needed.

The ultrasonic transducer is an electromechanical device. When a voltageis applied, a ceramic element is displaced to move air. The shape, mass,and applied voltage determine the displacement. Thus, sound is generatedby flexing a piezo electric element. The more voltage applied the morethe element is flexed. The more it is flexed the higher the output soundpressure level. Maximum applied voltage is 140 VPP at 40 kHz. Thisvoltage level generates a minimum 108 db SPL. Any voltage less than 140VPP generates less output.

The drive circuit 300 in one aspect includes a logic level field effecttransistor (FET) 306 to pulse a primary of a step up transformer.Transformer T1 302 is a step-up transformer that steps 8.75 V up to 140V. When Q5 has 5V applied to the gate of the transistor 306, PING_HI 140V is applied to the transducer element 304. When Q5 has 3V applied tothe gate of the transistor 306, PING_LO 80V is applied to the transducerelement 304. This provides two different maximum drive levels.

The secondary of T1 302 and the inherent capacitance of the transducer304 form a tank circuit with a Q>50 without R11 308 in place. The Q ofthe tank circuit determines how fast the transducer ramps up to fullsound pressure level. R11 308 programs the final Q of the circuit. Ingeneral, R11 308 determines how much energy is lost between excitationpulses and programs the transducer ramp.

Before the first excitation pulse, the transducer element 304 is a massat rest. A mass at rest tends to remain at rest. As such, the firstexcitation pulse does not yield maximum deflection of the transducerelement. Depending on how much energy R11 308 is lost between pulses,and the mass of the element, maximum deflection/voltage may never bereached or it may be reached from 2 to 8 pulses. Using two differentmaximum voltages with a known ramp up allows for the generation of anyoutput SPL up to the maximum. The FET 306 may be controlled by amicro-controller, which includes software that controls the pulsing ofthe transducer, thus controls output sound pressure levels withsoftware.

FIG. 4 is a flow diagram illustrating the method of controlling outputsound pressure level in an ultrasonic transducer in one embodiment ofthe present invention. At 402, micro-controller controlled FET is usedto pulse a primary step up transformer. For example, a step-uptransformer steps 8.75 volts up to 140 volts. Depending on the voltageapplied to the FET, up to 140 volts may be applied to the transducer.Thus, for example, having 3 volts applied at the gate of the FET willapply 140 volts to the transducer; having 5 volts applied at the gate ofthe FET will apply 80 volts to the transducer, providing two differentmaximum drive levels. At 404, a resistor determines how much energy islost between excitation pulses to determine the number of pulses neededfor the transducer to reach maximum voltage, and ultimately deflection.Accordingly, at 406, using two different maximum voltages with a knownramp up, a desired output sound pressure level up to the maximum isgenerated.

FIG. 5 is a communications system network diagram illustrating thesensor network in one embodiment of the present invention. Thecommunications system allows the sensors 504a to 504n in the network 500to be programmed at run time. FIG. 9 is a schematic diagram illustratingan individual sensor shown in FIG. 5. Referring to FIGS. 5 and 9, afirst sensor 504a in the network has its data input 506a tied, orelectrically connected, to a controller 502. The first sensor's dataoutput 508a, the drain of MOSFET Q1, is tied to the second sensor's datainput 506b. The second sensor's data output 508b is tied to the thirdsensor's data input 506c. All sensors 504a to 504n in the network 500are tied this way up to for example, 128 sensors in a daisy chainfashion.

Since diode D1 of Q1 is reversed biased, Q1 can operate as a high poweranalog switch. This switch can provide the serially connected sensors tooperate serially without complex readdressing wiring or algorithms ifthe sensors are relocated.

Initially, all sensors 504a to 504n in the network are turned off andtheir addresses are set to “$ff.” At power-up, only sensor 1504a, forexample, is electrically connected to the controller 502. All subsequentsensors 504b . . . 504n are isolated from the controller 502 and stillturned off. The connection with the controller 502 from these sensors504b . . . 504n are through the previous sensors. At power-up, thecontroller 502 directs the first sensor 504a to turn itself on andassigns the first sensor 504a an address. Using the address, thecontroller 502 then directs the first sensor 504a to direct the secondsensor 502b to turn itself on and assigns the second sensor 502b itsaddress. In this daisy chain fashion, the controller 502 turns on allthe sensors and assigns them addresses.

After power-up, the controller 502 polls the sensors 504a . . . 504n fortheir addresses. If an address of $ff is returned to the controller 502from any one of the sensors 504a . . . 504n, the controller 502 assignsa valid address. The controller 502 then turns on Q1 for the addressedsensors.

In one aspect, the returned addresses from the sensors when polled bythe controller 502 may be accumulated in a sensor array. The controller502 then addresses each element in the sensor array, and for each $ffaddress encountered in the sensor array, the controller assigns a validaddress to the sensor and turns on Q1 for the addressed sensor. Thisunique scheme of assigning addresses at runtime allows all sensors to beinterchangeable with one another. This is advantageous, for example,when a sensor installed in front of a vehicle needs to be moved to theback. The sensor being moved need not be individually reprogrammedbefore being installed at its new location.

In one aspect, each sensor's dimension is typically less than or equalto 55 mm (L)×25 mm (W)×20 mm (H). Active board area is about 9. squarecentimeters. These dimensions, however, may be altered. Sensors aretypically mounted about 30 inches above the ground, with appropriatespacing to cover the width of the surface. A single sensor may cover anarea of 1.5 meters by 3 meters.

Sensor response is unsolicited. Sensors respond to the host if a sensorerror occurred as a result of the last command or if a target wasdetected. If a sensor times out without finding a valid target it doesnot report so as not to burden the communications channel. Responses aresent to the controller in a form of designated bit patterns. Examples ofresponses from the sensors include:

-   -   $4c8014e0 Address zone 1 unit 4 found a target at 11 ft. 6 in.,        checksum is $e0.    -   $00016364 Address zone 6 unit 3 suffered a transducer error,        checksum is $64.

The above described invention can compensate for the attenuation changesby adjusting for changes in air temperature and changes in air density.Then the microcontroller can adjust for the speed of sound to calculatethe distance to an object.

While the invention has been described with reference to severalembodiments, it will be understood by those skilled in the art that theinvention is not limited to the specific forms shown and described.Thus, various changes in form and details may be made therein withoutdeparting from the spirit and scope of the invention as defined by theappended claims.

1. An ultrasonic sensor, comprising: a transducer for transmitting andreceiving sound waves; a drive circuit connected to the transducer fordriving the transducer to produce sound waves according to predeterminedsound pressure level; and a microcontroller connected to the drivecircuit for directing the drive circuit to produce a predeterminedamount of voltage, the amount of voltage determined as a function ofenvironment temperature and the predetermined amount of voltage directlyrelated to the predetermined sound pressure level.
 2. The ultrasonicsensor of claim 1, wherein the amount of voltage increases as theenvironment temperature increases.
 3. The ultrasonic sensor of claim 1,further comprising: a dynamic temperature model that allows gain on thereceived sound waves to be adjusted, the gain being adjusted as afunction of temperature.
 4. The ultrasonic sensor of claim 3, whereinthe gain increases as the temperature increases.
 5. The ultrasonicsensor of claim 3, wherein the dynamic temperature model includes an airdensity model and a gain model.
 6. The ultrasonic sensor of claim 5,wherein the gain increases as air density decreases.
 7. The ultrasonicsensor of claim 3, further comprising: an amplifier for adjusting thegain according to the dynamic temperature model.
 8. The ultrasonicsensor of claim 1, wherein the drive circuit comprises: a logic levelfield effect transistor; and a step up transformer connected to thelogic level field effect transistor that steps up voltage applied to thelogic level field effect transistor and applies the voltage to thetransducer.
 9. The ultrasonic sensor of claim 3, further comprising: acontroller, connected to the microcontroller, for receiving informationfrom the microcontroller about detected objects and alerting a user.